Gulf Coast clay and foundations

What the county is made of

The Handbook of Texas describes Fort Bend County as 869 square miles of level to gently rolling ground, 80 to 250 feet above sea level. Its soils run from rich alluvium in the Brazos valley to sandy loams and clays on the prairies. The Brazos crosses the county from northwest to southeast.

The Texas Almanac, drawing on USDA data, describes the Coast Prairie's upland soils as mostly deep, dark-gray clay loams and clays, on level land where surface water drains slowly.

Lake Charles clay

Lake Charles is one of the clay soils of the coastal prairie. The USDA's official description calls it very deep, moderately well drained and very slowly permeable, formed in clayey sediments of the Beaumont Formation, and says it's extensive in southeast Texas, mainly between the Colorado and Trinity rivers. When it dries:

• cracks 1/2 to 2 inches wide open at the surface and run a foot or more deep
• they stay open 60 to 90 days in most years
• undisturbed ground forms small mounds and hollows, with knolls about 6 to 15 inches (15 to 38 cm) higher than the low spots

Not every lot sits on Lake Charles clay. Brazos bottomland soils are different, and builders often bring in fill. Type your address into the USDA's free Web Soil Survey to see what's mapped there.

Why it matters for a slab

Clay that shrinks when dry and swells when wet doesn't move evenly under a house. Edges dry faster than the middle, and spots near trees or leaks behave differently from the rest. The Texas Section ASCE repair guidelines stress keeping soil moisture fairly even around the whole foundation, extending downspouts well past the slab into areas that drain, and avoiding overwatering.

What to watch for

• Diagonal cracks at door and window corners
• Doors that stick, swing or won't latch
• Cracked floor tile, or gaps opening at baseboards
• Soil pulling away from the slab edge in a dry spell

Photograph and date what you see. If it's getting worse, an engineer's evaluation tells you why.

Sources for this page

• Texas State Historical Association, Handbook of Texas: Fort Bend County (Virginia Laird Ott)
• Texas Almanac: Soils of Texas (source: USDA Natural Resources Conservation Service)
• USDA NRCS Official Soil Series Description: Lake Charles series (revised 03/2016)
• USDA NRCS Web Soil Survey
• Texas Section, American Society of Civil Engineers: Guidelines for the Evaluation and Repair of Residential Foundations, Version 3 (adopted April 1, 2022)

Checked October 7, 2026. Rules, prices and contact details change; confirm with the source before acting.